Were any scientific investigations conducted for proposing the theory? was this theory tested or simply expected?

C, h, o - elements that are common to biomolecules. if the biomolecule in question is a protein these elements also combine with nitrogen. which molecule below is a protein?

The kind of fertilization found in the majority of aquatic animals is (internal or external) fertilization.

The large increase in atmospheric carbon dioxide in the last 50 years most likely comes from a. an increase in cellular respiration b. increased decomposition by bacteria c. an increase in the burning of fossil fuels d. an increase in photosynthesis